1. Field of the Invention
The present invention relates to a motor control apparatus which converts AC power supplied from the AC input side into DC power, outputs the DC power to a DC link, further converts the DC power into AC power for driving a motor, and supplies the AC power to the motor, and a machine learning apparatus and method used for the motor control apparatus. More particularly, the present invention relates to a motor control apparatus including a protective operation control unit which instructs a motor to perform a predetermined protective operation upon power failure on the three-phase AC input side, and a machine learning apparatus and method used for the motor control apparatus.
2. Description of the Related Art
In a motor control apparatus which drives motors within a machine tool, a forging machine, an injection molding machine, an industrial machine, or various robots, AC power supplied from the three-phase AC input side is temporarily converted by a rectifier into DC power, which is further converted into AC power by an inverter. The AC power is used as drive power for a motor provided for each drive axis.
In such a motor control apparatus, when power failure occurs on the three-phase AC input side of the rectifier and the three-phase AC input voltage drops, it is no longer possible for the motor to continue normal operation. This may cause some type of trouble such as damage or deformation of, e.g., a motor, the motor control apparatus that drives the motor, a tool connected to the motor driven by the motor control apparatus, an object to be processed by the tool, or a manufacturing line including the motor control apparatus. Therefore, a power failure detection unit may be preferably set on the three-phase AC input side of the rectifier to monitor whether power failure has occurred on the three-phase AC input side of the rectifier. When the power failure detection unit determines that power failure has occurred on the three-phase AC input side of the rectifier, the motor control apparatus may preferably perform a protective operation for avoiding or minimizing the above-mentioned failure.
As a power failure detection method, as disclosed in, e.g., Japanese Laid-open Patent Publication No. 2006-14546, the three-phase AC input voltage on the AC power supply side of the rectifier is transformed by a coordinate transformation into an equivalent voltage vector on the two-phase coordinate system, and the amplitude of the vector is calculated to, in turn, calculate the amplitude value of the power supply voltage. When the amplitude value has been lower than a predetermined reference voltage value for a predetermined reference time, power failure is determined to be detected.
FIG. 7 is a block diagram illustrating a general motor control apparatus which performs a protective operation upon power failure. For the sake of illustrative simplicity, FIG. 7 illustrates driving of only one motor 104. A motor control apparatus 100 includes a rectifier 101 which converts AC power from a commercial three-phase AC power supply (to be simply referred to as an “AC power supply” hereinafter) 103 into DC power, an inverter 102 which is connected to a DC link (Direct-Current link) on the DC side of the rectifier 101, converts DC power output from the rectifier 101 into AC power having desired frequencies and supplied as drive power for the motor 104 or converts AC power regenerated from the motor 104 into DC power, and a DC link capacitor 105 is provided in the DC link and has a storage function for storing DC power and a smoothing function for suppressing pulsation of the DC output of the rectifier 101. The motor control apparatus 100 includes, as its control system, a normal operation control unit 111, a power failure detection unit 112, and a protective operation control unit 113. The normal operation control unit 111 controls, the inverter 102 to output AC power having desired voltages and frequencies for driving the motor 104 or convert AC regenerative power produced by the motor 104 into DC power, based on the AC current supplied from the inverter 102 to the motor 104, the DC voltage applied across the two terminals of the DC link capacitor 105 (to be simply referred to as a “DC link voltage” hereinafter), and the AC current supplied from the AC power supply 103 to the rectifier 101. The power failure detection unit 112 detects whether power failure has occurred, based on the power supply voltage on the AC power supply side of the rectifier 101. The protective operation control unit 113 sends a protective operation command to the inverter 102 to cause the motor control apparatus 100 to perform a protective operation when the power failure detection unit 112 detects that power failure has occurred. In response to the protective operation command, the inverter 102 converts the DC power stored in the DC link capacitor 105 into AC power preferably used for various protective operations for protecting, e.g., a tool connected to the motor 104, an object to be processed by the tool, and a manufacturing line including the motor control apparatus 100, and outputs the AC power.
A protective operation upon power failure advantageously allows protection of, e.g., a motor, a motor control apparatus, a tool, an object to be processed, and a manufacturing line including the motor control apparatus, but, once performed, it involves the stop of the manufacturing line and causes an economic loss. Therefore, upon power failure, the motor control apparatus and its peripheral devices (e.g., a control power supply unit and a coolant device) are preferably allowed to continue normal operation for a certain time, using energy stored in the DC link capacitor, to limit the execution of a protective operation to a preferable minimum time.